The general concept of a cavity receiver 5 for a solar central receiver system 10 can be described as follows. Sunlight is reflected from many mirrors (heliostats), such that most of the reflected sunlight is focused on one small area 15 at the top of a tower 20. At that location, the concentrated sunlight is allowed to pass through the aperture of a cavity. The intense solar radiation entering the cavity is then used to heat a material, usually a fluid. The heat absorbed by the fluid can then be used to generate power in a variety of ways.
A different design, called the solid particle receiver, was first conceived in the 1980s. In this design, the material being heated within the cavity is solid particles 25 rather than a fluid. In the tests conducted on this concept, the solid particles were released from a long narrow slot located at the top of the cavity and were allowed to fall freely, forming what may be called a “curtain”. The concentrated sunlight passing through the aperture was captured directly by the solid particle curtain. As a result, the temperature of the solid particles rose significantly. See, for example, FIG. 1.